Big difference seen between whites and blacks at age 45, but not at 85

Action Points

Blacks have a higher risk of stroke than whites when they're younger, but that risk fades over time -- and the risk of recurrent stroke is no different between groups over the course of a lifetime.

Note that the association of traditional stroke risk factors -- including hypertension, diabetes, cigarette smoking, atrial fibrillation, left ventricular hypertrophy, and heart disease -- was generally similar for first and recurrent stroke.

Blacks have a higher risk of stroke than whites when they're younger, but the extra risk diminishes with age -- and the risk of recurrent stroke is no different between groups over the course of a lifetime, researchers found.

In the REGARDS study, risk of first stroke was significantly higher for blacks than for whites at age 45 (HR 2.70, 95% CI 1.86-.91), but there was no racial disparity at age 85, George Howard, DrPH, of the University of Alabama at Birmingham, and colleagues reported online in Neurology.

And blacks didn't have a higher risk of recurrent stroke than whites at any time point (P>0.05), they found.

"This work documents a remarkably different association for first versus recurrent stroke for black race and age," the researchers wrote. "The substantial excess risk of incident stroke for 'young' (ages 45 to 65) black individuals was not present for recurrent stroke. Rather, the black-white differences in recurrent stroke risk were minimal."

A total of 29,682 patients from the Reasons for Geographic And Racial Differences in Stroke (REGARDS) study were included in the present analysis. All were 45 years of age and older and recruited between 2003 and 2007 from the general population. A total of 10% (2,993) reported having a physician diagnosis of stroke/TIA at baseline, while the remaining 90% did not have such a history.

Those with a history of stroke/TIA were more likely to be male, black, and to have stroke risk factors, the researchers said.

During an average follow-up of 6.8 years, 301 of the patients with a previous stroke at baseline had a recurrent stroke, while 818 of 26,689 participants (3.1%) who were stroke-free at baseline had a first stroke.

"The interplay of age and black race on stroke risk was remarkably different for first stroke compared to recurrent stroke," the researchers reported. Among those who were stroke-free at baseline, there was an age-by-race interaction (P=0.0002), with a first stroke risk 2.70 (95% CI 1.86–3.91) times greater for black than for white participants at age 45.

But that difference in risk diminished over time and was completely attenuated by age 85, and there was no evidence of race-by-age interaction for recurrent stroke at any time, they reported.

The study showed that at age 45, there was a 14.2-fold increased risk of recurrent stroke if a white participant had a previous stroke/TIA, while black participants had a 5.8-fold increased risk. This seems to imply the stroke risk associated with having a previous stroke is much larger for whites than blacks, but that's not the case, the researchers said.

The apparent larger effect of a previous stroke on risk of recurrent stroke in white versus black individuals is due to the fact that risk of first stroke is substantially lower in whites than blacks, they explained. "Hence at older ages, the stroke risk associated with having had a previous stroke is relatively small and similar for black and white individuals," they wrote.

In an interview, Howard said the researchers were surprised to learn that the association of traditional stroke risk factors -- including hypertension, diabetes, cigarette smoking, atrial fibrillation, left ventricular hypertrophy, and heart disease -- was generally similar for first and recurrent stroke. This pattern was confirmed with longer follow-up, they reported.

"We thought stroke risk factors would play a smaller role in recurrent stroke," Howard told MedPage Today. Since the data didn't bear this out, this "means that physicians need to prevent and treat risk factors both to avoid a first stroke and also to avoid a second stroke."

The study was limited by its reliance on self-reported stroke events that occurred before participants were enrolled in the study. On the other hand, REGARDS had a large study population and events during follow-up were adjudicated by physician review of medical records, the researchers said.

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